1. Meiosis

2. What is Meiosis?
Meiosis is the process that allows the amount of DNA to reduce by half when a cell divides.
Why would we need this process?
Reproduction! The mom and dad have to give the baby ½ of its new DNA.
Meiosis produces gametes - sex cells such as eggs, sperm, pollen, etc.
This process is similar to mitosis because it uses similar phases but it goes through those phases twice.

4. Chromosome Numbers What do humans have? Types of cells
46 chromosomes in a normal cell (diploid)
23 chromosomes in a haploid gamete (ex: sperm or egg)
Types of cells
Diploid – there are two of each type of chromosome
Haploid – there is one of each type of chromosome

6. Diploid vs. Haploid
Diploid (2n)
Haploid (n)

7. Chromosome Structure
Homologous chromosomes – these are chromosomes that have genes on them that code for the same thing
Same length
Same centromere location
Carry genes for the same thing
Sister chromatids – these are identical copies of the same chromosome

8. Phases of Meiosis 1 Interphase DNA is copied and proteins are made
Prophase 1
1st true stage of meiosis
sister chromatids condense to form synapsis
Crossing over occurs here (chromosomes “trade” small segments)
Metaphase 1
The pairs of homologous chromosomes line up in the middle of the cell
Anaphase 1
The joined sister chromatids move to opposite ends of the cell
The chromosome number reduces from 2n to n.
Telophase 1
Sister chromatids are at the poles and the cell divides.

9. Meiosis 1

10. Phases of Meiosis 2 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2
Spindle apparatus forms
Chromosomes condense
Metaphase 2
A haploid number of chromosomes line up in center
Anaphase 2
Sister chromatids move away from center to poles of the cell
Telophase 2
Chromosomes reach the poles and the nuclei reform

11. Meiosis video: http://tinyurl.com/ktaafgo

12. Meiosis 2

13. Cytokinesis
After both phases of meiosis have occurred, the cell divides into four haploid cells which are gametes.

14. Meiosis Animation Link
Click the link below. Once the page loads, click the “animation” tab. Next be sure the narration button has been pressed and the animation will begin. It explains and shows you what meiosis is and how it occurs.

15. Mitosis vs. Meiosis Mitosis Meiosis How many phases? One Two
Synapsis of homologous chromosomes? No
During prophase 1
What is created?
Two identical diploid (2n) cells
Four non-identical haploid(n) cells
Type of cells produced
Somatic (body) cells
Gametes (sex) cells
Why do we need it?
To repair cells and allow for growth of the individual
Gametes are used for sexual reproduction

16. Asexual Reproduction
Asexual reproduction does not require meiosis because the organism inherits all its chromosomes from its parent.
Bacteria reproduce asexually.
Some plants and simple animals reproduce asexually
Most plants and all complex organisms reproduce sexually.

17. Mendelian Genetics
Gregor Mendel – an Austrian monk who did research using pea plants to investigate heredity.
He used pea plants because they were easy to breed, provided lots of offspring, and were easy to care for.
He became the “father of genetics” due to his research.

18. How did he do it?
Female pistil
Pea plants have both male and female parts on the same flower. Normally they self pollinate.
He would cut away male parts before the flower matured so he could control pollination.
Male stamen

19. He used a paint brush to transfer pollen from one plant to another.

20. Mendel’s Monohybrid Cross
He used “purebreeding” parents for his P1 or parent generation. He crossed plants with green and yellow peas.
When he crosspollinated the flowers, all his offspring were….
YELLOW!

21. So…He crossed those yellow peas.
Mendel crossed his F1 generation of pea plants and when he did, he got…
¾ yellow peas and ¼ green peas
Yellow seed color is dominant to green color. Y y YY Yy yy Y y

22. Dominance, recessive, homozygous, heterozygous… what does it all mean?
Dominant – masks the recessive trait.
Recessive – it can be present but you will not see it. (many genetic diseases are recessive)
Homozygous (purebred) – If both alleles are the same (ex: YY or bb)
Heterozygous (hybrid) – If the alleles for a trait are different (ex: Yy or Bb)

23. Genotype vs. Phenotype
Phenotype: The physical appearance of an organism
Genotype: Yy or YY – the genetic letters that represent the genes of the organism

24. Punnett Squares
You can use the genotype of the parents to determine the possibilities for the offspring.
Ex: A female seal with long whiskers (WW) mates with a male seal with short whiskers (ww).

25. More Examples…
Mendel crossed two heterozygous tall parents (Tt). Complete a punnett square showing the possible offspring. What percentage will be tall?_____ What percentage will be short? ____

26. In the guinea pig, black fur (B) is dominant over brown fur (b)
In the guinea pig, black fur (B) is dominant over brown fur (b). If a homozygous black guinea pig is crossed with a heterozygous black guinea pig, what are the chances that the offspring will be brown?

27. Mendel’s First Law: The Law of Segregation
Mendel discovered that parent organisms give one allele to each gamete. This means that they segregate or “separate” their genes, giving each gamete only one copy.
(2:34)

28. Mendel’s Second Law: the Law of Independent Assortment
Mendel determined that alleles for each trait join randomly to create random offspring.
(6:35)

29. Gene Linkage and Polyploidy
Genetic recombination – makes new combinations of genes.
Gene linkage – if genes are close together on a chromosome, they are said to be “linked” because they are inherited together.

30. Polyploidy
Polyploidy is the occurrence of one or more extra sets of all chromosomes in an organism.
A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes.